GWEN IFILL: Another school was engulfed by sudden violence today, when a teenager stabbed and slashed 19 students and a security guard in Pennsylvania. It happened just minutes before classes began at Franklin Regional High, in Murrysville, about 20 miles east of Pittsburgh.

The 16-year-old suspect was finally wrestled down. Police didn’t release his identity, but did say he was armed with two knives.

Emergency officials said a fire alarm may have limited the casualties.

DAN STEVENS, Westmoreland County Emergency Management: We’re teaching children in school now if they’re in a hallways and they hear something going on to basically run out of the building.

Pulling that fire alarm could have saved lives, without a doubt, to make people think that something going on, to get out of the building. One person’s actions could have saved 10 people’s lives or caused 10 people not to be injured.

GWEN IFILL: Several of the wounded were in critical condition, including one with a deep wound that narrowly missed his heart.

At Fort Hood, Texas, today, the commander in chief and the troops remembered the victims of last week’s mass shooting. They gathered at a somber ceremony that’s become all too familiar.

For the second time in five years, the nation’s largest Army base honored soldiers killed not in wars abroad, but by a gunman from within their own ranks.

As before, President and Mrs. Obama were there.

PRESIDENT BARACK OBAMA: Once more, soldiers who survived foreign war zones were struck down here at home, where they’re supposed to be safe. We still do not know exactly why. But we do know this. We must honor their lives, not in word or talk, but in deed and in truth.

GWEN IFILL: The shooter, 34-year-old specialist Ivan Lopez, opened fire at the base last Wednesday, after an argument over a leave request.

Today, helmets and boots marked the three soldiers who died: Sergeants Timothy Owens, Carlos Lazaney-Rodriguez, Daniel Ferguson. Lopez also wounded 16 others before taking his own life.

It was over in eight minutes, but the president said, the grief endures.

PRESIDENT BARACK OBAMA: I know that the men and soldiers they became, their sense of service and their patriotism, so much of that came from you. You gave your sons to America, and just as you will honor them always, so, too, will the nation that they served.

GWEN IFILL: Today’s service took place on the same site as in November 2009, when Mr. Obama last visited Fort Hood. That was five days after Major Nidal Hasan shot and killed 13 people, in the worst mass murder ever at an American military installation.

Now, as the community grieves again, leaders are left to ponder what else they can do. There was no talk today from the president of new initiatives against such violence. Instead, it was a day reserved for comforting words, amid the echoing refrain of mourning.

The agents who guard the president have new rules about taking a drink. There was word today that the Secret Service has tightened its alcohol policy after a pair of embarrassing incidents. The Washington Post reports the agency also demoted the head of the Special Operations Division and reassigned nearly two dozen agents.

A string of bombings killed dozens of people from Syria to Pakistan today, and wounded scores more. The state news agency in Syria reported two car bombs exploded in the central city of Homs, killing 25 people. In Iraq, car bombs killed at least 24, and left burned vehicles littering the streets in Shiite districts of Baghdad and a town to the south. And, in Pakistan, a bomb tore through a busy produce market on the outskirts of Islamabad. At least 21 people were killed in that attack.

In Ukraine, the government warned it won’t wait forever to end standoffs in two eastern cities. Pro-Russian separatists are still occupying regional government buildings in Donetsk and Luhansk and still demanding votes on declaring independence.

In Kiev, the interior minister said he — his government wants the confrontations resolved within the next two days.

ARSEN AVAKOV, Interior Minister, Ukraine (through interpreter): I am sure that both political and force options are available. But it seems like another option will be taken up, which is something in between. For those who want dialogue, we propose talks and a political solution. For the minority who want conflict, they will get a forceful answer from the Ukrainian authorities.

GWEN IFILL: In Washington, Assistant Secretary of State Victoria Nuland said there’s no doubt the Russians were directly involved in the unrest in Eastern Ukraine. And Secretary of State John Kerry spoke twice by phone with the Russian foreign minister.

Optimism rose today among Australian officials leading the search for that missing Malaysian jetliner. That’s after they picked up two more pings that may very well have come from the plane’s black box recorders.

Lucy Watson of Independent Television News reports from Beijing. Many of those on the plane were Chinese citizens.